Scanning electron microscope

ABSTRACT

A secondary electron signal obtained from a specimen when the specimen is scanned with an electron beam is detected by a detector and a specimen image is displayed on a first display screen area of an image display unit on the basis of the detected signal. The specimen image is stored, as an image for observation position designation, in a storage unit together with a position of the image. A plurality of images at different positions on the specimen may be used as the image to be stored. One of the stored images is selected and read and displayed on a second display screen area. When a part of interest on the displayed image for observation position designation is selected, the specimen is horizontally moved so that a position of the part of interest may be positioned at the center of the first display screen area and an enlarged image of the part of interest may be displayed on the first display screen area. This facilitates view field search outside a view field range.

This is a continuation of U.S. patent application Ser. No. 08/987,308,filed Dec. 9, 1997 now U.S. Pat. No. 6,225,628.

BACKGROUND OF THE INVENTION

The present invention relates to a scanning electron microscope forobtaining an image of a specimen by detecting an information signalwhich is generated by scanning the specimen with an electron beam andwhich is characteristic of the specimen.

In a scanning electron microscope, with the aim of moving a positiondesignated on an image to a predetermined position and obtaining anenlarged image corresponding to the designated position, a technique asdescribed in JP-A-54-78075 has been known in which a desired positioninside an observation view field is designated by a display pointer anda specimen is moved to the center of the observation view field.

This technique is effective when a position to be observed while beingenlarged is within the observation view field. But when the position tobe enlarged and observed is outside a view field range or outside a beamscanning permissible region, an enlarged image corresponding to thatposition cannot be obtained.

In general view field (or observation position) search, it is frequentthat a position to be observed which is not only inside an observationview field but also outside a view field range is searched. Accordingly,approximate positioning is first carried out on an image at amagnification effective for view field (or observation position) searchand thereafter, the magnification is gradually increased to determine anobservation position and an observation magnification. However, theposition search method as above lacks the function of marking anobservation position and is difficult to achieve when observation is tobe again effected at the same position.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a scanning electronmicroscope suitable for facilitating search for an observation positionwhich is outside a view field range.

To accomplish the above object, a scanning electron microscope accordingto the present invention comprises means for generating an informationsignal characteristic of a specimen by scanning the specimen with anelectron beam, means for detecting the generated information signal,means for obtaining an observation image of the specimen on the basis ofthe detected information signal, means for storing the obtainedobservation image as an image which is used to designate observationposition, means for reading the stored image for observation positiondesignation, means for displaying the obtained observation image and theread-out image for observation position designation on individualdisplay screen areas, means for designating an observation position onthe displayed image for observation position designation, and means forcontrolling a position of the specimen scanned with the electron beamsuch that the designated observation position is moved to apredetermined position on the display screen area for the observationimage and an observation image corresponding to the designatedobservation position is displayed on that display screen area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing the construction of a scanningelectron microscope according to an embodiment of the present invention.

FIG. 2 is a flow chart showing, as an example, specimen observation.

FIG. 3 is a graph showing, as an example, a map of coordinate positionson specimen stage of stored images.

FIG. 4 is a diagram showing, as an example, an image display.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1 schematically showing the construction of ascanning electron microscope according to an embodiment of the presentinvention, an electron beam 2 emitted from a cathode 1 is drawn by drawvoltage V1 applied across the cathode 1 and a draw electrode 3 andaccelerated by accelerating voltage Vacc applied across the cathode 1and an accelerating electrode 4. The electron beam 2 is focused on aspecimen 9 carried on a specimen stage 10 by means of condensing lenses5 and 6 and an objective lens 8 which are controlled by a lens controlpower supply 12. The specimen stage 10, accordingly, the specimen 9 canbe moved in horizontal directions (X and Y directions) and in the axialdirection of the electron beam 2 (Z direction) and can be rotated bymeans of a specimen stage drive unit 19. A scanning signal from a scancontrol unit 26 is applied to a two-stage deflector consisting ofdeflectors 7 a and 7 b, so that the specimen 9 is scannedtwo-dimensionally with the focused electron beam. Denoted by 11 is anaperture.

An information signal characteristic of the specimen 9, typically, asecondary electron signal 13 is generated from the specimen 9 under theirradiation of the electron beam 2. The generated secondary electronsignal 13 is detected by a signal detector 14 a and/or 14 b. Either oneor both of the detectors are used depending on the kind of the specimenand the height thereof. The signal detected by the detector 14 a and/or14 b is guided, in the form of a brilliance modulation signal, to animage display unit 15 including a cathode ray tube (CRT). Although notillustrated in the figure, scanning in the CRT of the image display unit15 is synchronous with the scanning of the specimen 9 with the electronbeam 2 and consequently, an enlarged image (scanning image) of specimen9 due to secondary electrons is displayed on real time base. Themagnification of the enlarged image can be set desirably by means of themagnification setter 27.

Referring to FIG. 2 showing a flow of specimen observation, an enlargedimage of the specimen 9 is first displayed on the image display unit 15in the aforementioned manner (S1). When the enlarged image is designatedby a storage image control unit 17 (S2), a signal indicative of thedesignated enlarged image is stored in a storage unit 16, together witha position on the specimen (a coordinate position on the specimen stage)corresponding to a position on the enlarged image (actually, a centerposition of the enlarged image) (S3). Of course, by executing thedesignation by plural times, a plurality of enlarged images at differentpositions on the specimen can be stored in the storage unit 16.

A map of coordinate positions on specimen stage of stored images isillustrated in FIG. 3, and it may be displayed on the image display unit15 in place of enlarged images of the specimen or alternatively, may bedisplayed separately. In the figure, positions on specimen 21 of thestored images are displayed in the form of position display pointers.When one of the position pointers is selected and designated by thestorage image control unit 17, a stored image corresponding to thedesignated position is read (S4) and displayed, as an image which isused to designate observation position, on the image display unit 15simultaneously with an enlarged image of the specimen obtained on realtime base (S5).

Referring to FIG. 4, an example of display is shown in which theenlarged image of the specimen obtained on real time base is displayedon a display screen area 22 of the image display unit 15 and at the sametime the image read out by the designation and serving as an image whichis used to designate observation position is displayed on a partialdisplay screen area 23 of the area 22. In FIG. 4, a position displaypointer 28 indicates a position of a part of the enlarged image desiredto be observed while being enlarged. When the specimen stage 10 isrotated, the image for observation position designation is rotatedcorrespondingly, and when the specimen stage 10 is rotated to move anobservation position, the position display pointer 28 is movedcorrespondingly to the rotation direction and the movement. In FIG. 4,the image for observation position designation is displayed on the area23 forming a part of the display screen area 22 but alternatively, maybe displayed on a different area or side by side the enlarged image.

When a part of interest of the image displayed on the area 23, that is,the image for observation position designation is selected anddesignated by operating a position designator 28 (S6), a position signalof that designated part is read out of the storage unit 16 and suppliedto the specimen stage drive unit 19. As a result, the specimen stage 10,accordingly, the specimen 9 is moved horizontally (to perform so-calledview field or observation position movement) so that the position of thedesignated part may automatically be positioned at the center positionof the display screen area 22 (S7), with the result that an enlargedimage of the designated part (observation image) is displayed on thedisplay screen area 22 to permit observation of the designated part(S8). The magnification of the enlarged image can be set freely by meansof the magnification setter 27.

As will be seen from the foregoing, view field search can beaccomplished by reading a stored image for observation positiondesignation and hence the work of search for an observation positionoutside the view field range can be facilitated. Further, in addition tothe image for observation position designation, a position thereof isalso stored and therefore, position setting for re-observation can alsobe facilitated. Further, since the view field (observation position)search can be accomplished by reading a stored image, damage of thespecimen due to the electron beam can be mitigated.

When the image for observation position designation is stored in thestorage unit 16, an accelerating voltage, focusing conditions of thelenses, that is, exciting conditions and working distances (WD's) of thelenses 5, 6 and 8 at the time that the image is obtained may also bestored in the storage unit 16 in addition to the image for observationposition designation and the position signal of the image. In this case,when the image for observation position designation is read, anaccelerating voltage and focusing conditions and working distances ofthe lenses corresponding to the read-out image can be read andautomatically set by means of a control unit 24. In an alternative, whenthe image for observation position designation is read, the excitingcurrent of the objective lens may be controlled by the control unit 24so as to bring the objective lens into in-focus.

Concurrently with the storage of the image for observation positiondesignation in the storage unit 16, use conditions of the detectors 14 aand 14 b may also be stored. In this case, when the image forobservation position designation is read, use conditions of thedetectors 14 a and 14 b corresponding to the read-out image may also beread and set automatically by means of the control unit 24.

One or more positions on the image for observation position designationdisplayed on the display screen area 23 and images at highermagnification than that of the displayed image for observation positiondesignation and corresponding to those positions may be stored in thestorage unit 16. In this case, the stored positions on the displayedimage for observation position designation are displayed in the form ofposition display pointers on the displayed image, and storedhigher-magnification images at those positions may be read bydesignating the displayed positions so as to be displayed on the displayscreen area 22.

An image for observation position designation to be stored in thestorage unit 16 may be an image of a linkage of images obtained byscanning divisional areas of the specimen with the electron beam. Thisis effective for observation of an area which is wider than the scanningpermissible range.

According to the present invention, the scanning electron microscopesuitable for facilitating view field or observation point search outsidethe view field range can be provided.

What is claimed is:
 1. A scanning electron microscope comprising: acathode; a condensing lens for focusing an electron beam emitted fromsaid cathode; a scanning deflector for scanning a specimen with saidelectron beam; a detector for detecting electrons emitted from saidspecimen by the electron beam scanning; a storage unit for storingcoordinate information as a plurality of points represented by a storedcoordinate map, enlarged images and/or a beam condition data adjustingthe electron beam per points on said map; a display unit for displayingan image of said specimen on the basis of electronic signals obtained bysaid detector; means for displaying a pointer indicative of a portionobserved with a magnification larger than said image of the specimen bysuperimposing said pointer on said image of the specimen displayed onsaid display unit; a control unit for designating the pointer on saiddisplay unit so as to provide one of the enlarged images of thedesignated pointer on said display unit; a specimen stage for movingsaid specimen; and means for moving said pointer displayed on saiddisplay unit in accordance with the move of said specimen stage.
 2. Ascanning electron microscope comprising: a cathode; a condensing lensfor focusing an electron beam emitted from said cathode; a scanningdeflector for scanning a specimen with said electron beam; a detectorfor detecting electrons emitted from said specimen by the electron beamscanning; a storage unit for storing coordinate information as aplurality of points represented by a stored coordinate map, enlargedimages and/or a beam condition data adjusting the electron beam perpoints on said map; a display unit for displaying an image of saidspecimen formed on the basis of electronic signals obtained by saiddetector and a pointer indicative of a portion of the image of saidspecimen stored in the storage unit in association with the coordinateinformation in superimposing said image and said pointer; a specimenstage for moving said specimen; and a control unit for designating saidpointer on said display unit so as to provide the enlarged image portionof the designated pointer on said display unit and for moving saidpointer displayed on said display unit in accordance with the move ofsaid specimen stage.
 3. A scanning electron microscope comprising: acathode; a condensing lens for focusing an electron beam emitted fromsaid cathode; a scanning deflector for scanning a specimen with saidelectron beam; a detector for detecting electrons emitted from saidspecimen by the electron beam scanning; a display unit for displaying animage of said specimen on the basis of electronic signals obtained bysaid detector; a memory for storing position signals indicative ofspecific positions on said specimen, enlarged images and/or a beamcondition data adjusting the electron beam per points on said map; aspecimen stage for moving said specimen; and a control unit forcontrolling to display pointers on said image of the specimen displayedby said display unit on the basis of said position signals stored insaid memory and for designating the pointer on said display unit so asto provide one of the enlarged images of the designated pointer on saiddisplay unit.
 4. A scanning electron microscope according to claim 3,wherein specific images of the specimen at said specific positions arememorized in said memory and wherein one of said images of the specimenat said specific positions is read out on the basis of selection of saidpointers displayed on the image of specimen displayed on said displayunit.